What characterizes depolarization, the first phase of the action potential? the membrane potential changes to a less negative (but not a positive) value. the membrane potential changes from a negative value to a positive value. the membrane potential reaches a threshold value and returns to the resting state. the membrane potential changes to a much more negative value.

Option (2).

Explanation:

The cell potential or membrane potential may be defined as the difference in the electric potential between inside and outside of the cell. The membrane potential of the cell changes during the propagation of action potential.

The resting membrane potential is -70mV. The influx of sodium ions causes the depolarization of the cell membrane. The cell potential changes from -70mV to + 30mV. The membrane potential becomes more positive during the depolarization phase.

Thus, the correct answer is option (2).

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.

explanation: